STM32L431 can not be debugged; SWD communication failure?

ZJing · ‎2022-12-01

Hello all,

I am using STM32L431 in this project, and I have made a prototyping board for it. However, the MCU will not communicate with the debugger.

Below is MCU part of schematic:

Only SWDIO and SWCLK are connected to the debugger. The MCU is powered seperately by an on board LDO.

Error message:

I tried to reset by pressing S1 after powering up, but that did not work.

I initially left VDDA unconnected to 3V3 while all VDDs are connected to 3V3, by not mouting BEAD L1. Now the L1 pads are shorted with solder. Could this have damaged the MCU?

Power supply schematic:

The typical design of this LDO suggested using output capacitor of 1uF, while I am using 4.7. However, they did mention that using output capacitors larger than 1uF is possible.

Please help! Thanks in advance!

ZJing · ‎2022-12-02

Hello @Jaroslav JANOS,

Thanks for the reply.

This is a cheap debugger from China, it only comes with SWD. This debugger has been used with their STM32L431 development board without any problems. We are going to order a ST-Link, but it might not be the debugger's fault.

Best regards,

Zhi